Table of Contents
What Is Young's Modulus?
Young's modulus (E) measures stiffness -- resistance to elastic deformation. It equals stress/strain. High E = stiff material. Steel (200 GPa) is 3× stiffer than aluminum (69 GPa). Named after Thomas Young (1807), it is fundamental to structural engineering.
E determines beam deflection, cable stretch, and structural rigidity. It applies only in the linear elastic region where deformation is reversible.
Stress-Strain Formula
E in Pascals, σ = stress (Pa), ε = strain (dimensionless).
Material Stiffness
| Material | E (GPa) |
|---|---|
| Diamond | 1,050 |
| Steel | 200 |
| Copper | 117 |
| Aluminum | 69 |
| Bone | 14 |
| Rubber | 0.01-0.1 |
Frequently Asked Questions
Stiffness vs strength?
E = stiffness (resistance to deformation). Strength = maximum stress before failure. Glass is stiff but brittle. Rubber is flexible but withstands large strains.
Temperature effect?
Higher temperature weakens atomic bonds, reducing E. Steel drops from 200 GPa at 20°C to ~150 GPa at 600°C -- critical for fire engineering.
What is Poisson's ratio?
Ratio of lateral to axial strain when stretched. Most metals ~0.3. Rubber ~0.5 (incompressible). Cork ~0 (no lateral change).